Solid state imaging devices are currently used in a wide range of applications including, for example, video movies and monitoring cameras. Optical communications techniques have been widely used in various fields. Such devices depend on opto-electrical integrated circuits that are fabricated on a substrate such as a semiconductor wafer. In an opto-electrical integrated circuit used in an optical information processing system, various optical components, such as a light-emitting device and a micro lens, are formed integrally on the substrate. This minimizes the space required for the optical components and optimizes performance.
In optical communications, optical signals are transmitted through optical fibers. Generally, use is made of an optical switching device for changing the transmission path of optical signals from one fiber to another. To attain proper data transmission, operation of the switching device requires a large data-handling capacity, high-speed data transmission and high stability, for example. Therefore, it is preferable that an optical switching device incorporate a micromirror unit which is fabricated using a micro-machining technique. The use of a micromirror obviates the need to convert an optical signal to an electrical signal in performing the switching operation between the data input path and the data output path of the switching device.
One widely-used method for manufacturing micro lenses is the molding polymerization method. In the molding polymerization method, polymer powder is placed into a lens mold and hot-pressed to form a substrate with a micro-lens array. Although this method is cost-effective and simple, manufacture of a mold having the desired micro-lens curvature is an extremely difficult task, particularly in cases in which the lenses have an irregular shape and small size (less than about 0.5 micron meter). Accurate control of focus length requires a time-consuming adjustment process carried out by highly-skilled personnel.
Another common method for manufacture of micro-lenses is the ion exchange diffusion method. In such a method, a mask layer having a desired pattern is formed on a transparent, flat glass substrate. The substrate and mask layer is immersed in a salt solution bath. Positive ions such as sodium and potassium cations contained in the substrate are exchanged with positive ions such as titanium cations contained in the salt solution. The ion-exchanged regions in the substrate have a different refractive index from the original refractive index of the glass, and thus, form refractive index distribution regions having a light-refracting action. The ion exchange diffusion method, however, is not economical on a wide scale since the mask layer must be formed on each individual substrate.
Another conventional method used to fabricate micro-lenses is shown in FIGS. 1A-1E. In FIG. 1A, a substrate 10, which is GaAs, is provided. A silicon dioxide film 12 is formed on the substrate 10, and a photoresist layer 14 is deposited on the silicon dioxide film 12. As shown in FIG. 1B, the silicon dioxide film 12 of FIG. 1A is then subjected to a dry etch process to define an etching mask 16 that conforms to the pattern of the photoresist 14. As shown in FIGS. 1C and 1D, in a reactive ion beam etch (RIE) step, the substrate 10 is then subjected to a chlorine ion beam 18, which etches the substrate 10 according to the pattern defined by the etching mask 16. As shown in FIG. 1E, the chlorine ion beam 18 eventually etches the etching mask 16 from the substrate 10, leaving a micro-lens 20 on the region of the substrate 10 which was shielded by the etching mask 16. In a variation of the process, the substrate 10 is etched in a wet etch process.
One of the limitations of the conventional methods of fabricating micro-lenses is that the methods are incapable of being used to fabricate lenses having a large size (100 μm and greater). Accordingly, a novel method is needed for the large-scale fabrication of micro-lenses having a size of 100 μm or greater.
An object of the present invention is to provide a novel method of fabricating micro-lenses having a variety of sizes.
Another object of the present invention is to provide a novel spherical structure patterning method for fabricating a micro-lens.
Another object of the present invention is to provide a novel micro-mirror fabrication method which is suitable to fabricate micro-lenses on a large scale.
Still another object of the present invention is to provide a novel micro-lens array fabrication method in which a lens mold is fabricated, followed by fabrication of a micro-lens in the lens mold.
Yet another object of the present invention is to provide a novel micro-mirror fabrication method which is suitable to fabricate micro-lenses having a width or diameter of at least 100 μm, as well as micro-lenses of smaller size.
A still further object of the present invention is to provide a novel micro-lens fabrication method which includes providing a convex photoresist surface, forming a lens mold on the convex photoresist surface, removing the lens mold from the convex photoresist surface, and molding a micro-lens in the lens mold.
Yet another object of the present invention is to provide a novel micro-lens array manufacturing method in which multiple lens molds can be simultaneously fabricated on a substrate by curing a photoresist coating on the substrate and multiple micro-lenses can be fabricated in the respective lens molds.
A still further object of the present invention is to provide a novel micro-lens manufacturing method which is applicable to manufacturing micro-lenses suitable for a variety of applications.
Another object of the present invention is to provide a novel micro-lens having a generally transparent lens body that is formed by providing a convex photoresist surface, forming a lens mold on the convex photoresist surface, removing the convex photoresist surface from the lens mold, forming the lens body in the lens mold and removing the lens mold from the lens body.